Bear minimum:
A) ester oil
B) new drier with XH9 desiccant
C) R134a virgin refrigerant
D) R134a charge port adapters, in some cases you may need to replace
the York manifolds to obtain ease of access to service fittings
Better:
E) new barrier hose lines
Thinking ahead:
F) 507 compressor; if you have an old York the cost to repair can be rather expensive
Ideal:
G) adding more condenser area, upgrading evaporator and blower motor
Good reading material that can be transferred to the 912:
The Mr. Ice Project